Method of purifying zinc-bearing solutions.



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FREDERICK LAIS'JE AND JAMES ORR ELTON, OF ANACONDA, MONTANA, ASSIGNORS T0 ANACONDA COPPER MINING CGMPANY, 0F ANACONDA, MONTANA, A. CORPORATION OF MONTANA.

manages. lilo Drawing.

]Bearing Solutions, of which the following is a specification.

Zinc-bearing solutions, such'ror example as those prepared by leaching calcined zinc ores with dilute sulfuric acld, are readily purified from iron, and from a part at least of their content of arsenic and antimony. This may beaccomplished for example by effecting a complete oxidation of the iron salts in the solution, and then precipitating the same by such basic reagents as z1nc oxid or lime; under these conditions arsenic and antimony are largely prec1p1tated with the ferric iron, as disclosed for example in the prior patents to Laist and lFr'ick, Numbers 1,167,700 and 1,167,701. The resulting solutions however, usually carry other impurities, notably copper and cadmium, the comable difiiculties. On the other hand such complete elimination is a practical necessity, inasmuch as the presence of these metals even in very small proportions tends to reduce the current efliciency in the subsequent electrolytic deposition of zinc, and

tends also to a poorer quality of deposit.

We have found that zinc sponge, prepared by electrolytic precipitation from zinc salt solutions, is a highly efficient agent for all) the treatment or impure zinc-bearing solutions, especially for the separation there from of traces of copper and cadmium. As hereinafter pointed out this zinc sponge may be prepared by electrolyzing pure zinc salt solutions, in which case a pure zinc sponge is obtained; or it may be prepared by electrolysis of the solutions which are to be purified, in which case a double result is achieved, to wit, the solutions from which the sponge is precipitated are purified either wholly or in part; and zinc sponge is obtained in suitable condition for the treat ment of the same or other zinc-bearing solutions.

lln-either case zinc anodes are used, which are electrolytically dissolved, thereby maintainingnormal conditions in'the electrolyte Specification. of Letters Iatent.

METHOD 01E PURIFYING ZINC-BEARING SOLUTIONS.

Patented. Feb. 5, 11ml.

Application filed .Tune 16, 1916. Serial No. 104:,083.

as regards acidity and concentration. According to the voltage and current density employed, the zinc sponge may separate out upon the cathodes, or upon the bottom of the cell, or it may remain suspended in the electrolyte; or it may appear in any two or in all of these conditions. Our invention is therefore not restricted to the employment of any specific electrical conditions, although we have found it desirable to use voltages between 0.5 and 2.3, the corresponding current densities lying between 2 and 30 amperes, per square centimeter of active electrode surface. These conditions may, however, be considerably varied, providedonly a fine spongy deposit is obtained. At the lower voltages mentioned above more of the sponge tends to collect upon the bottom of the cell, where it is immediately available for use.

This sponge may be directly used Without drying, the solution to be purified being thoroughly agitated therewith, after which the excess of zinc is permitted to settle out from the solution, and is reused so long as it retains its efiiciency.- When it becomes too high in copper and cadmium, it. may be refined in any known manner for the recovery or its components.

Or the wet sponge may be dried under strictly non-oxidizing conditions, for example in a current of any inertgas, or in oacuo, after whlch 1t is available for use in the electrical conditions being controlled to effect the deposition of zinc as sponge as specified above. If the rate of flow of the solution is sulficiently slow, its complete purification may be accomplished in the course or its passage through the electrolytic 'cell, and the sponge is then available for the treatment either of other solutions or or other portions or the same solution. It

; however, the flow is maintained at a rate in excess of that at which complete purificationis obtainable, the'precipitated zinc sponge may be carried forward'into an agitator in the line of flow of the solution from the electrolytic cell," ahd is used to complete the purification of this solution;

By proceeding in this way we secure a rapid and substantially complete purification of the solution with a minimum use of zinc and a minimum expenditure of power. 'In this operation we prefer to employ voltages of a comparatively low range,tp'referably below those required for the. deposition of zinc .with insoluble anodes.

lVe prefer to employ one, or preferably more, combination agitating and settling, tanks operating as follows: The tanks are charged with the zinc sponge, oriwithzinc 1 dust or sludge from any. other source if such be available, in large excess of theamount actually required for the-purification of the solution.-, In these tanksjthe solution is thoroughly agitated with the zinc until the purification is complete or has proceeded'as far as is necessary, after which the. agitator is stopped and the excess of zinc, together with the separated impurities is permitted to subside: The clear solution is nowdra'wn' off, and the above operation repeated with further quantities of solution to be purified, until the zinc is exhaustedor its efficiency lost. By proceeding in thisway the usual heavy wastage of zinc is avoided. Any suitable type of apparatus may be used for this purpose, as for example a tank of the ordinary Pachuca type, provided with an eflicient stirrer, and with a draw-off above they conical bottom for the clearsolution. Such apparatus is well lmown in the art and need not be further described.

A further modification 'of the invention consists in subjecting the zincbearing solution which is to be purified, to the action of zinc anodes, the current conditions being so regulated that little or'no zinc is deposited in the form of sponge or otherwise,

the electrodeposi tion being substantially or wholly restricted to the more electro-neg'ative components of the. solution usually including copper and cadmium. ln this way, operating with low'current densities, the solution may be more or less completely purified depending upon its rate of flow through the cells. The precipitated impurities will settle upon the bottom of the cell asa sludge, deposit upon the cathodes, or be held in suspension in the electrolyte from which they may be removed by any appropriate clarifying means, as by filtration or settling.

' We claim 1. Ina process of purifying zinc-bearing solutions, the step which consists in subjectmg the impure solutions to the action of electrolytically deposited zinc sponge.

2. A process of purifying zinc-bearing solutions and recovering metallic zinc, which consists in passing an electric current through the impure solution from anode surfaces of zinc to purify the solution, and

thereafter electrodepositing zinc from the purified solution.

3. A process of purifying zinc-bearing solutions, which consists in passing an electric current-through the impure solution from anode surfaces of zinc under conditions to forma deposit of'zinc sponge.

4. A process of purifying zinc-bearing solutions, which consists in passing an electric current'through-the impure solution from 'anode surfaces of zinc under-conditions to agitating the partially purified solution in the presence of finely divided zinc to complete the purificatiom In testimony whereof, we aflix our signatures. v

FREDERICK LAIST. JAMES ORR ELTON. 

